Various developments have been made on conductors containing carbon materials (such as carbon fibers, carbon nanotubes, and graphenes) and electrical devices using the conductors including photoelectric conversion devices (such as solar cells, organic EL devices, and optical sensors).
The carbon material can be used to greatly reduce the usage of a rare metal or the like. The carbon material is excellent in flexibility, mechanical strength, and chemical stability. The carbon material has a relatively high conductivity and exhibits a high resistance in intermolecular conduction. A large-area transparent electrode containing the carbon material has a higher electrical resistance as compared with those containing an indium tin oxide (ITO) film having the same light transmittance. In addition, the carbon material exhibits a higher electrical resistance in a long-distance electrical wire or the like as compared with conductive metal materials containing copper or the like. Therefore, composites of the carbon material and a particle or wire of a metal or semiconductor have been studied in view of improving the conductivity.